1. Field of the Invention
The present invention relates to an optical pickup for recording and reproducing information with respect to an optical disk. More particularly, the present invention relates to an objective-lens driving device and a mechanism for adjusting the inclination of an objective lens which are aimed at making the optical pickup compact and thin and stabilizing the driving of the objective lens in both a focusing direction and a tracking direction.
2. Description of the Related Art
In general, an optical pickup is comprised of an objective-lens driving device having an objective lens and an optical system block for transmitting and receiving light with respect to the objective lens, and is structured such that the objective-lens driving device is mounted on a mounting base of the optical system block.
To accurately effect the recording and reproduction of information with respect to an optical disk, it is necessary to accurately set the optical axis of the objective lens perpendicular to the disk surface.
For this reason, a mechanism for adjusting the inclination of an objective lens is conventionally known (e.g., Unexamined Japanese Patent Application (Kokai) No. 62-287443) which is arranged as follows: As shown in FIG. 1, a spherically convex mounting surface 103 is made to project from a bottom surface 102a of an objective-lens driving device 102 having an objective lens 101. In addition, as shown in FIG. 2, a spherically concave mounting surface 106 is formed in a mounting base 105 of an optical system block 104, the spherically convex mounting surface 103 is fitted in the spherically concave mounting surface 106, and the inclination of the objective lens 101 is made adjustable with respect to the center (fulcrum) 107 of a sphere formed by the spherically convex mounting surface 103 and the spherically concave mounting surface 106 by means of height adjusting screws 108.
However, since the spherically convex mounting surface 103, the spherically concave mounting surface 106, and the height-adjusting screws 108 are disposed between the objective-lens driving device 102 and the mounting base 105 of the optical system block 104, the thicknesswise dimension becomes large, thereby constituting a hindrance to the attempt to make the optical pickup thin.
In addition, to accurately effect the recording and reproduction of information with respect to an optical disk, it is necessary to prevent the occurrence of unwanted resonance. To prevent the occurrence of such unwanted resonance, in a conventional objective-lens driving device 201A shown in the perspective view in FIG. 3, the position of the center of gravity of a movable section 204, which has an objective lens 202, a focusing coil 203A for a focusing direction Z, and a pair of tracking coils 203B for a tracking direction Y, is aligned with an optical axis 205, and the central axes of the focusing coil 203A and the tracking coils 203B are aligned with the optical axis 205 (e.g., Unexamined Japanese Patent Application (Kokai) No. 2-230522).
The optical pickup having this arrangement is capable of preventing the occurrence of unwanted resonance, but it is necessary to dispose a light source, a reflecting mirror, a light-receiving element, and the like below the objective-lens driving device to effect the recording and reproduction of information. Hence, it has been difficult to make the optical pickup compact and thin.
To make the objective-lens driving device compact and thin, in a conventional objective-lens driving device 201B shown in the exploded perspective view in FIG. 4, the central axes of a focusing coil 208A and a pair of tracking coils 208B are not aligned with the optical axis 205, and the focusing coil 208A and the tracking coils 208B are disposed in a magnetic gap 207 provided in a single magnetic circuit 206 (e.g., Unexamined Japanese Patent Application (Kokai) Nos. 4-102235 and 4-103038).
In addition, in the objective-lens driving device disclosed in Unexamined Japanese Patent Application (Kokai) 4-103038, to accurately drive the movable section in the direction of the optical axis (focusing direction), a focusing-driving force which is provided outside the magnetic gap is minimized, so as to prevent an unnecessary force, such as moment, from acting in the movable section. It has been thought that this focusing-driving force occurring outside the magnetic gap, i.e., the leakage flux density, should be suppressed to as low a level as possible partly for preventing interference with metallic parts such as a motor disposed in the vicinity of the objective-lens driving device.
In addition, although the conventional objective-lens driving device 201B shown in FIG. 4 is capable of making the optical pickup compact and thin, there is a drawback in that, if an attempt is made to adjust the position of the center of gravity to either one of the driving points, the other driving point is offset from the position of the center of gravity, so that unwanted resonance occurs on the offset side.
FIG. 5A shows a schematic arrangement of an optical disk apparatus portion in a magneto-optic recording/reproducing system, in which an optical disk 301 is provided with an optical pickup 304 having a magnetic head 302 on one side and an objective lens 303 on the other side. The magnetic head 302 and the optical pickup 304 are driven in the radial direction of the optical disk 301 by a head driving device 305 and a feed motor 306, respectively, and the optical disk 301 is rotated by a spindle motor 307. Among such optical disk apparatuses, those of a type in which the optical disk 301 is covered with a cartridge 308 for the purpose of protecting the optical disk 301 have come to be marketed in recent years. This cartridge-type optical disk is arranged as follows: As shown in FIG. 5B, the optical disk 301 is rotatably accommodated in a space formed between an upper shell 308a and a lower shell 308b, and the shells 308a and 308b are provided with windows 308c and 308d, respectively. When the optical disk 301 is not in use, the windows 308c and 308d are closed by a shutter 308e, and, during recording or reproduction, the shutter 308e is moved laterally to open the windows 308c and 308d and insert the magnetic head 302 and the objective lens 303 into the windows.
In the conventional optical pickup 304, as described in, for example, Unexamined Japanese Patent Application (Kokai) 61-139945, a circuit for driving the objective lens 303 in the focusing direction and the tracking direction is disposed at a position other than that below the objective lens 303, whereby a free space is formed below the objective lens 303, and a reflecting mirror is disposed at that position, thereby making the overall optical pickup 304 thin.
With such a conventional apparatus, as shown in FIG. 6A, the optical disk 301 and the objective lens 303 are opposed to each other with an interval L33 therebetween so that the optical axis of the objective lens 303 aligns with a central portion, as viewed in the rotating direction of the disk, of the window 308d of the lower shell 308b. In this arrangement, however, since a magnetic circuit 309 for effecting the positional adjustment of the objective lens 303 in the focusing and tracking directions is disposed outside the window 308d, there arises a need to provide a gap L31 between a lower surface of the lower shell 308b and an upper surface of a yoke 310 constituting the magnetic circuit 309. As a result, the distance L32 between the lower surface of the lower shell 308b and the lower surface of the magnetic circuit 309 becomes large, thereby constituting a hindrance to making the optical pickup 304 thin and compact.
FIG. 7 shows an exploded perspective view of a conventional objective-lens driving device (Unexamined Japanese Patent Application (Kokai) No. 3-212826).
A conventional objective-lens driving device 401 shown in the drawing is arranged as follows: A lens holder 403 with an objective lens 402 affixed thereto is cantilevered by being soldered onto a printed circuit board 409 in which four wires 404 inserted in an intermediate member 405 are secured to the intermediate member 405. The intermediate member 405 is mounted on a yoke base 406.
Incidentally, the printed circuit board 409 and the four wires 404 are electrically connected to each other. Electric current is allowed to flow across a focusing coil 407A and a pair of tracking coils 407B, which are arranged in the holder 403, via these four wires 404, to thereby drive the objective lens 402 in the focusing direction Z and the tracking direction Y.
To accurately effect the recording and reproduction of information with respect to the optical disk, it is necessary to prevent the occurrence of unwanted resonance.
For this reason, as shown in FIG. 8, a damping-member accommodating portion 405a is formed in the intermediate member 405, and a gel damping member 408 is filled in the accommodating portion 405a. 
However, as for the conventional objective-lens driving device 401, since the intermediate member 405 is attached to the yoke base 406, and a printed circuit board 409 is secured to the intermediate member 405 by means of screws or the like, the number of component parts used is large. Hence, there has been a problem in that if the respective component parts are fixed by means of an adhesive, the number of assembling steps increases, so that the fabrication is not facilitated.
In addition, if the printed circuit board 409 is secured to the intermediate member 405 by means of screws, there have been cases where both ends of the printed circuit board 409 at portions remote from the wires 404 become lifted off due to changes in temperature and aged deterioration, as shown in FIG. 9. Hence, the four wires 404 are respectively deflected or conversely pulled, and the supporting balance becomes deteriorated, thereby resulting in changes in the angle of the optical axis of the objective lens 402 and unwanted resonance. Further, in cases where the yoke base 406 and the intermediate member 405, and the intermediate member 405 and the printed circuit board 409 are secured separately, if the bottom surface of the yoke base 406 is set as an assembling reference plane A, as shown in FIG. 10, there has been a problem in that it is difficult to set a B surface of the printed circuit board 409 perpendicular to the reference plane A, thereby making it impossible to drive the objective lens 402 with high accuracy.
The present invention has been devised in view of the above-described circumstances, and it is an object of the present invention to provide a mechanism for adjusting the inclination of an objective lens which makes it possible to make an optical pickup thin.
Another object of the present invention is to provide an objective-lens driving device which makes it possible to make an optical pickup compact and thin and drive the objective lens stably in both the focusing direction and the tracking direction.
Still another object of the present invention is to provide a cartridge-type optical disk apparatus having a structure which makes it possible to make the optical disk apparatus thin and compact.
A further object of the present invention is to provide an objective-lens driving device which is easy to manufacture and is capable of driving the objective lens with high accuracy.
In accordance with a first aspect of the present invention, there is provided a mechanism for adjusting the inclination of an objective lens for use in an optical pickup including an objective-lens driving device, having an objective lens, and an optical system block for transmitting and receiving light with respect to the objective lens, the objective-lens driving device being mounted on a mounting base of the optical system block. In the adjusting mechanism, a recessed portion or a through hole portion is formed in the mounting base of the optical system block, a projecting portion of a bottom of the objective-lens driving device is accommodated in the recessed portion or the through hole portion, and an inclining fulcrum for inclining the objective lens and height adjusting means for inclining the objective-lens driving device about the inclining fulcrum are provided in vicinities of the recessed portion or the through hole portion of the mounting base.
In accordance with a second aspect of the present invention, there is provided a mechanism for adjusting the inclination of an objective lens for use in an optical pickup including an objective-lens driving device, having an objective lens and a yoke, and an optical system block for transmitting and receiving light with respect to the objective lens, the objective-lens driving device being mounted on a mounting base of the optical system block. In the adjusting mechanism, a movable plate with a substantially U-shaped cross section which is formed integrally with the yoke is provided, a recessed portion or a through hole portion is formed in the mounting base of the optical system block, a lower portion of the yoke formed integrally with the movable plate is accommodated in the recessed portion or the through hole portion, and an inclining fulcrum for inclining the objective lens and height adjusting means for inclining the objective-lens driving device about the inclining fulcrum are provided in vicinities of the recessed portion or the through hole portion of the mounting base.
In accordance with a third aspect of the present invention, in the mechanism for adjusting the inclination of an objective lens according to the second aspect of the invention, the height adjusting means includes an urging member for upwardly urging the objective-lens driving device from the mounting base of the optical system block, and a screw for tightening the objective-lens driving device against the mounting base of the optical system block.
In accordance with a fourth aspect of the present invention, there is provided an optical disk apparatus in which a magnetic circuit of the objective-lens driving device is disposed within a window area of a lower shell of the optical disk. In a case where such a structure is adopted, to prevent the demagnetization of the optical disk, it is preferred that optical disk-side opposite ends of a yoke constituting the magnetic circuit of the driving device for driving an objective lens be magnetically short-circuited by a magnetic member.
In accordance with a fifth aspect of the present invention, there is provided an optical disk apparatus in which opposite end portions, as viewed in a tracking direction, of an objective lens holder which are opposed to the disk are formed into inclined surfaces, so as to prevent the lens holder from colliding against an edge on the innermost peripheral side or outermost peripheral side of the window in the lower shell, and to prevent an increase in the vertical dimension of the lens holder. In addition, in the optical disk apparatus in which such inclined surfaces are formed at the opposite end portions, as viewed in the tracking direction, of the objective lens holder which are opposed to the disk, the magnetic circuit of the objective-lens driving device is preferably disposed within the window area of the lower shell of the optical disk, and a portion of the objective lens holder which opposes a side edge of the window in the lower shell is preferably formed into an inclined surface.
In accordance with a sixth aspect of the present invention, there is provided an objective-lens driving device comprising: a movable section including an objective lens, a focusing coil, and a tracking coil; and a fixed section which includes a single magnetic circuit having a magnetic gap and in which the focusing coil and the tracking coil are both disposed in the magnetic gap, wherein a point of application of a resultant force of a focusing-driving force generated by a magnetic flux in the magnetic gap and a reversely-oriented focusing-driving force generated outside the magnetic gap by a magnetic flux leaking from the magnetic gap is brought close to a point of application of a tracking-driving force by controlling an amount of leakage magnetic flux.
Furthermore, the weight of the movable section is distributed such that a position of a center of gravity of the movable section is located between the point of application of the tracking-driving force and the point of application of the resultant force of the focusing-driving forces.
In accordance with a seventh aspect of the present invention, there is provided an objective-lens driving device comprising: a movable section including an objective lens, a focusing coil, and a tracking coil; and a fixed section which including a single magnetic circuit having a magnetic gap, both of the coils being disposed in the magnetic gap, wherein a point of application of a tracking-driving force, a point of application of a resultant force of focusing-driving forces respectively occurring in and outside the magnetic gap, and a position of a center of gravity of the movable section are made to substantially coincide with each other.
In accordance with an eighth aspect of the present invention, there is provided an objective-lens driving device comprising: a movable section including an objective lens and a coil for generating a driving force in a predetermined direction; a resiliently supporting member serving as a path for supplying electric current to the coil and supporting the movable section in a cantilevered manner or on both sides thereof; a printed circuit board electrically connected to at least one fixed end side of the resiliently supporting member; and a base having a yoke for generating the driving force; and an intermediate member for fixing the printed circuit board and the base by molding in a state in which the printed circuit board and the base are positioned relative to each other.
In accordance with a ninth aspect of the present invention, in the objective-lens driving device according to the eighth aspect of the invention, the intermediate member has a guide hole for inserting the resiliently supporting member therethrough to connect the fixed end side of the resiliently supporting member, and a damping-member accommodating portion for accommodating a damping member for damping unwanted resonance of the movable section is formed in a vicinity of the guide hole.
In accordance with the mechanism for adjusting the inclination of an objective lens according to the first aspect of the invention, the fulcrum for inclining the objective lens and the height adjusting means are provided in the vicinities of the recessed portion or the through hole portion formed in the mounting base of the optical system block, and it is thereby possible to make the optical pickup thin.
In accordance with the mechanism for adjusting the inclination of an objective lens according to the second aspect of the invention, since the yoke and the movable plate are formed integrally, the optical pickup can be made thin, and since the yoke and the movable plate are formed integrally, the fabrication is facilitated.
In accordance with the mechanism for adjusting the inclination of an objective lens according to the third aspect of the invention, the objective-lens driving device can be inclined about the fulcrum for inclining the objective lens in accordance with the degree of tightening of the screw, thereby inclining the objective lens.
In accordance with the objective-lens driving device according to the fourth aspect of the invention, since the magnetic circuit is disposed within the window in the lower shell, the dimension between the lower surface of the magnetic circuit of the driving device and the lower surface of the lower shell can be reduced, thereby making it possible to obtain a thin device. In addition, according to the fifth aspect of the invention, since the radially opposite end portions of the objective lens holder, which are opposed to the disk, are formed into inclined surfaces, it is possible to make the lens holder thin.
In accordance with the objective-lens driving device according to the sixth aspect of the invention, since the point of application of the resultant force of focusing-driving forces respectively occurring in and outside the magnetic gap is brought close to the point of application of the tracking-driving force, their distances with respect to the position of the center of gravity of the movable section can both be reduced. Therefore, it is possible to easily prevent the occurrence of unwanted resonance in both the focusing direction and the tracking direction. Furthermore, since the position of the center of gravity of the movable section can be located between the point of application of the tracking-driving force and the point of application of the resultant force of the focusing-driving forces respectively occurring in and outside the magnetic gap, the distances between the position of the center of gravity of the movable section and the point of application of the resultant force and between the position of the center of gravity of the movable section and the point of application of the tracking-driving force are both made short. Therefore, it is possible to prevent the occurrence of unwanted resonance in both the focusing direction and the tracking direction.
In accordance with the objective-lens driving device according to the seventh aspect of the invention, the focusing coil and the tracking coils are disposed in the magnetic gap, so that the objective-lens driving device can be made compact and thin. In addition, since the point of application of the tracking-driving force and the position of the center of gravity of the movable section are made to substantially coincide with each other, it is possible to make the device compact and thin. Hence, it is possible to realize a stable servomechanism in which unwanted resonance does not occur in both the focusing direction and the tracking direction.
In accordance with the objective-lens driving device according to the eighth aspect of the invention, since the printed circuit board and the base are secured to each other by being positioned relative to each other when the intermediate member is formed by molding, a bonding process and a screw-tightening process can be omitted in assembling the printed circuit board, the base, and the intermediate member. Hence, the relative positional accuracy between the printed circuit board and the base can be improved.
In accordance with the objective-lens driving device according to the ninth aspect of the invention, since the damping member is accommodated in the damping-member accommodating portion, the damping member suppresses the vibration of the resiliently supporting member, thereby damping the unwanted resonance of the movable section.